A threat launch detection system is a system that detects a weapon being directed at a target, with the target typically containing the threat launch detection system. In response to detecting a weapon directed at the target, which will be referred to as a threat or event throughout the present description, the threat launch detection system typically takes countermeasures to prevent the weapon from impacting the target. For example, an airplane may include a threat launch detection system designed to detect missiles fired at the airplane. When the system detects a missile, the system typically takes appropriate countermeasures in an attempt to prevent the missile from impacting the airplane, such as transmitting a signal to “jam” electronic circuitry in the missile that is guiding the missile towards the target.
A conventional threat launch detection system is illustrated in FIG. 1, which more specifically depicts a block diagram of a directional infrared countermeasures (DIRCM) system 100. The system 100 includes a missile warning system 102 that detects the presence of weapon or threat 104 directed at an airplane or other vehicle (not shown) containing the DIRCM system. In the example of FIG. 1, the threat 104 is a missile that has been fired at the airplane containing the DIRCM system 100. The missile 104 includes a guidance system (not shown) for sensing infrared energy emitted by the airplane and for directing the missile towards the airplane.
The missile warning system 102 is typically a passive system that includes a sensor array (not shown) in combination with suitable optics (not shown) to provide a relatively wide field of view WFOV for missiles 104. The wide field of view WFOV is the region of space surrounding the system 100 in which missiles 104 can be detected. The sensor array in the missile warning system 102 is typically an array of infrared (IR) sensors that capture a series of images within the field of view WFOV. Processing circuitry (not shown) in the missile warning system 102 analyzes the captured images to detect a threat and generates a coarse directional determination indicating an arrival angle at which the missile or other threat 104 is approaching an airplane containing the system 100.
The missile warning system 102 provides this determined arrival angle to a system controller 106 which, in response to the determined angle, applies signals to a fine tracking system 108 to begin positioning a fine track sensor (not shown) toward the target at the determined angle. More specifically, this fine track sensor in the system 108 is typically mounted on a gimbal (not shown) that rotates in response to the signals from the system controller 106 to direct the fine track sensor towards the determined angle and thereby toward the approaching missile 104. The fine track sensor has a narrow field of view NVOV that is much smaller than the wide field of view WFOV to allow the fine tracking system 108 to precisely track the missile 104 or other threat positioned within the narrow field of view.
The fine tracking system 108 further includes a jamming laser (not shown) that is also directed towards the missile 104 by the rotating gimbal. Once the gimbal has positioned the fine track sensor and jamming laser towards the missile 104, the jamming laser is turned on and infrared laser energy from the laser illuminates the approaching threat 104 missile. This infrared laser energy is modulated in such a way that the when the guidance system in the missile 104 senses this energy the guidance system directs the missile away from the airplane. The fine tracking sensor in the fine tracking system 108 senses the position of the missile 104 during this time to accurately illuminate the missile 104 with energy from the jamming laser.
The process of providing the determined angle of the approaching missile 104 to the fine tracking system 108 via the controller 106 and subsequent positioning of the fine track sensor and jamming laser may be referred to as a “handoff” or “transitioning” from the missile warning system to the fine tracking system. This is true since directional information from the missile warning system 102 is transitioning to the fine tracking system 106 to allow the fine tracking system to determine precise directional information for the missile 104 and thereby allow the jamming laser to successfully “jam” the guidance system of the missile. In this way, the fine tracking system 106 tracks the missile 104 and jams the guidance system of the missile. Note that typically the sensors in the missile warning and fine tracking systems 102 and 108 do not operate in the same waveband, with the missile warning system typically operating in the ultraviolet waveband the fine tracking system typically operating in the infrared waveband. This need not be the case and in the future the missile warning system 108 too may operate in the infrared waveband. Note that a fire from an engine propelling the missile 104 shows up in both the ultraviolet and infrared frequency spectrums or wavebands. Also note that due to the much larger field of view WFOV of the missile warning system 102 when compared to the field of view NFOV of the fine tracking system 108, the resolution of images captured by the missile warning system is much lower than the resolution of images captured by the fine tracking system.
Current missile warning systems 102 have sophisticated algorithms to analyze the series of captured images and distinguish true targets 104 from false ones or from clutter that is constantly being sensed due to background objects within the wide field of view WFOV. In this context, clutter may be viewed as data in each captured image that is other than data corresponding to the target or threat. The fine track sensor in the fine tracking system 108, however, is much less sophisticated and does not have historical record in the form of a series of captured images for the threat 104 within the narrow field of view NFOV. As a result, the fine tracking system 108 does not have a series of images to compare at handoff from the missile warning system 102. This means that while the missile warning system 102 may accurately determine the existence and arrival angle of the threat 104, the fine tracking system 108 may select a false threat or a clutter object within the narrow field of view NFOV. A false selection of a false threat or clutter object means the jamming laser in the fine tracking system 108 may not properly illuminate the approaching threat 104 and could lead to the threat not being properly countered. Certain systems 100 may have major issues with transitioning or handing off a threat 104 from the missile warning system 102 to the fine tracking system 108, particularly under conditions of high clutter or with low contrast targets.
The narrow field of view NFOV of the fine tracking system 108 is generally much greater than the effective divergence of the jamming laser in order to mitigate errors in arrival angle information that is transferred or handed off from the missile warning system 102. Such errors in arrival angle information can result from a variety of different factors, such as misalignment between sensors in the missile warning system 102 and fine tracking system 108. This misalignment can be static or be dynamic and due to such things as flexure of the airplane between the location of the missile warning system 102 and the fine tracking system 108. Non-linear characteristics across elements in the sensor array in the missile warning system 102 may also result in errors in arrival angle information.
There is a need for improved methods and systems for transitioning a threat from the a missile warning system to a fine tracking system in DIRCM systems, especially under conditions of high clutter or low contrast targets or threats.